Electrical contacts



8, 1956 L. TQRICHARDSON ETAL 2,760,257

ELECTRICAL CONTACTS Original Filed Dec. 3, 1949 United States Pate ELECTRICAL CONTACTS Linwood T. Richardson, Wauwatosa, and Merle R. Swinehart, Milwaukee, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a-corporation of Delaware Continuation of application Serial No. 131,034, December 3, 1949, now abandoned. This application February 11, 1953, Serial No. 336,293

9 Claims. '(Cl. 29-1825) This invention relates to imp-rovements in powder composition electrical contacts and more particularly to contacts composed of silver, cadmium oxide and nickel sulphate.

The present application is in continuation of our application, Serial No. 131,034, filed December 3, 1949, now abandoned.

As is well known to those skilled in the art, electrical contact elements heretofore have been subject to many limitations. Excessive arcing, pitting of the contact surfaces, tarnishing, transferof metal between contacts, welding and sticking are but a few of the difiiculties encountered. One or more of these diificulties may become troublesome accordingly as the contacts are subjected to electrical contacts which are capable of making and breaking circuit a large number of times while carrying relatively high currents.

Another and more specific object of this invention is to provide improved electrical contacts which will make and break 2000 amperes of a 28 volt'rdirect current resistance load in-excessof one hundred times.

Anotherobject is to-provide electrical contacts of novel composition, whereby such contacts when made of normal size and shape and make and break 2200 amperes of a 250 volt, 60 cycle, 50% lagging power factor load, at least 100 times.

A further object is to provide electrical contacts of the aforementioned character which have a high resistance to pitting and bonding or welding.

Other objects and advantages of the invention will hereinafter appear.

The single figure of the accompanying drawing is a highly magnified fragmentary sectional view of an electrical contact embodying our invention.

As a result of extensive experiments we have found that the desirable characteristics of a contact formed of a bonded mass of powdered silver and cadmium oxide can be greatly improved by incorporating therein a quantity of nickel sulphate. Nickel sulphate when added in varying amounts to a mixture of powdered silver and cadmium oxide, the whole of which is then compressed and sintered, produces contacts which are capable of repeatedly making and breaking circuits carrying relatively high currents and which further are particularly characterized by their resistance to pitting and their ability to maintain a smooth contact surface.

Patented Aug. 28, 1956 The relative proportions of the powdered silver, cadmium oxide and nickel sulphate may be varied within certain ranges for the purpose of adapting the contacts to suit certain requirements. For example, a pair of electrical contacts, three-fourths of an inch in diameter, formed of a bonded mass of per cent by weight of .powdered silver, 21.25 per cent by weight of cadmium oxide and 3.75 per cent by weight of nickel sulphate, were found to be capable of making and breaking 2200 amperes of a 250 volt, 60 cycle, 50% lagging power factor alternating current load at least times. After testing, these contacts showed no signs of failure and were found to have retained a smooth contact surface with no evidence of pitting or sticking.

For maximum life with moderate alternating currents, contacts having a composition of 82 per cent by weight of powdered silver, 16.77 per cent by weight of cadmium oxide and 1.23 per cent by weight of nickel sulphate were found to be particularly desirable. Apair of contacts of this latter composition, three-fourths of an inch in diameter, showed no signs of failure and retained their smooth surface after being used to make 300 amperes and break 50 amperes of a 250 volt, -60 cycle, 50% lagging power factor alternating current 260,000 times.

Nickel sulphate was also found to greatly improve the ability of electrical contacts to make and break large direct currents. A pair of contacts three-fourths of an inch in diameter and composedof a bonded mass of 87.5 per cent by weight of powdered silver, '10 ,per cent by weight of cadmium oxide and 2.5 per cent by weight of nickel sulphate were found capable of making and breaking 200 amperes of a 28 volt direct-current resistance load at least 50,000 times with no evidence of failure or pitting. Another pair of contacts of similar size and composition were found capable of making and breaking 2000 amperes of a 28 volt direct current resistance load 9,500 times before they failed by adhering to each other.

As hereinbefore mentioned, the relative proportions of powdered silver, cadmium oxide and nickel sulphate may be varied over a certain range. Although less than 1.23 per cent by weight of nickel sulphate will greatly improve the desirable characteristics of silver-cadmium oxide contacts, its addition in the amount of from 1.23 per cent to 3.75 per cent by weight of the entire mass-of the contact composition has been found to be most desirable. The silver content may vary from 75 to 93 per cent by weight, and the cadmium oxide content may vary from 3.25 to 23.77 per cent by weight.

The drawing illustrates the manner in which the nickel sulphate is intermixed with the silver and cadmium oxide of our contacts. Numeral 1 designates a highly magnified fragment of one of our improved contacts. A base or matrix material 2 consisting of compressed and sintered powdered silver has intermixed therethrough particles 3 which are composed of a compressed and sintered mixture of nickel sulphate and cadmium oxide.

The following is a preferred method of making our improved contacts. However, it is to be understood that this method is set forth by way of example only, it being assumed that other methods of producing contacts having a similar structure and composition will be readily suggested to those skilled in the art.

An intimate mixture of the desired or required proportions of nickel sulphate and cadmium oxide (each ingredient being in the form of a powder of such fineness that the mixture will pass through a 325 mesh screen) is densified by applying a molding pressure of the order of 100,000 pounds per square inch. The slugs produced in this manner are then subjected to a temperature of 1600 degrees F. for a period of one hour, after which they are ground in such a manner, or to such an extent, that all of the particles thereof will pass through a 100 mesh screen and approximately one-half of the total quantity of said particles will be retained on a 300 mesh screen.

The particles produced in the above-described manner are then intimately mixed with a given quantity oi precipitated silver powder. This mixture is subjected to that degree of cold molding pressure which will result in the maximum sintered density for the particular type and lot of silver powder being used, the pressure t from 25,000 to 40,000 pounds per squa inch. ll molding operation produces preforms which are then subjected to a temperature of approximately 1600 degrees F. for about twenty minutes. After such heat treap ment, the preforms are subjected to a final moldi pres sure of approximately 100,000 pounds per square inch to produce the completed electrical contacts.

We claim:

1. A compressed and sintered electrical contact for by weight of nickel sulphate, said cadmium oxide and nickel sulphate being in mixture form and distributed jointly as discrete particles throughout the mass of silver.

2. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of from seventy-five to ninety-three per cent by Weight of silver powder, from three and one-fourth to twenty-three and seventy-seven hundredth per cent by Weight of cadmium oxide, and from one and twenty-three hundredths up to three and seventy-five hundredths per cent by weight of nickel sulphate.

3. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of from seventy-five to ninety-three per cent by weight of silver powder, from three and one-fourth to twenty-three and seventy-seven hundredths per cent of cadmium oxide, and from one and twenty-three hundredths up to three and seventy-five hundredths per cent by weight of nickel sulphate, said cadmium oxide and nickel sulphate being in mixture form distributed jointly in the form of discrete particles throughout the mass of silver.

4. An electrical contact for making and breaking an electric circuit, said contact being formed of compressed and sintered silver powder containing distributed therethrough discrete particles composed of a compressed and sintered mixture of nickel sulphate and cadmium oxide, said nickel sulphate constituting approximately three and three-fourths per cent by weight of the whole mass of the contact and said cadmium oxide constituting approximately ten per cent by Weight of the whole mass of the contact.

5. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of from seventy-five to ninety-three per cent by weight of silver powder having dispersed therein as discrete particles a compressed and sintered mixture of from three and one-fourth to twenty-three and seventyseven hundredths per cent by weight of the complete contact of cadmium oxide, and from one and twenty-three hundredths to three and three-fourths per cent by weight of the complete contact of nickel sulphate.

6. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of eighty-two per cent by weight of powdered silver, sixteen and seventy-seven hundredths per cent by weight of cadmium oxide, and one and twenty-three hundredths per cent by weight of nickel sulphate.

7. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of seventy-five per cent by weight of powdered silver, twenty-one and one-fourth per cent by weight of cadmium oxide, and three and three-fourths per cent by weight of nickel sulphate.

8. An electrical contact in the form of a compressed and sintered mass of powdered silver having distributed therethrough discrete particles each of which is composed of a compressed and sintered mixture of from one and twenty-three hundredths per cent to three and threefourths per cent by weight of nickel sulphate and from three and one-fourth to twenty-three and seventy-seven hundredths per cent by weight of cadmium oxide.

9. An electrical contact in the form of a bonded mass of powders composed of a compressed and sintered mixture of eighty-seven and one-half per cent by weight of powdered silver, ten per cent by weight of cadmium oxide, and two and one-half per cent by weight of nickel sulphate, said cadmium oxide and nickel sulphate being jointly in the form of compressed and sintered discrete particles distributed throughout the mass of silver.

References Cited in the file of this patent UNITED STATES PATENTS 2,080,811 Emmert May 18, 1937 2,390,595 Larsen et a1. Dec. 11, 1945 2,418,811 Adams et a1. Apr. 15, 1947 2,425,052 Swinehart Aug. 5, 1947 

1. A COMPRESSED AND SINTERED ELECTRICAL CONTACT FOR MAKING AND BREAKING AN ELECTRIC CIRCUIT, FORMED OF AT LEAST SEVENTY-FIVE PER CENT BY WEIGHT OF SILVER POWDER, ABOUT TWENTY-ONE AND ONE-HALF PER CENT BY WIEGHT OF CADMIUM OXIDE, AND ABOUT THREE AND ONE-HALF PER CENT BY WEIGHT OF NICKEL SULPHATE, SAID CADMIUM OXIDE AND NICKEL SULPHATE BEING IN MIXTURE FROM AND DISTRIBUTED JOINTLY AS DISCRETE PARTICLES THROUGHOUT THE MASS OF SILVER. 